The structure, function and evolution of repeated genes or their gene products are being studied in the ciliated protozoan, Tetrahymena pyriformis. The structure of chromatin containing the genes for 25S and 17S ribosomal RNA and for 5S RNA is being probed with the aid of non-specific deoxyribonucleases. The properties of chromatin and of the histones of genetically active macronuclei and of genetically inert micronuclei are being compared utilizing nuclease digestion, circular dichrosim and continuous variation, peptide mapping and automated protein sequencing. A system has been developed for studying the induction of tubulin gene expression which occurs during cilia regeneration in starved Tetrahymena. It is hoped that these studies will shed light not only on the organization, evolution and function of the particular repeated genes being studied, but also on general mechanisms which regulate the differential expression of genes in eukaryotic cells.